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1. Introduction
1.1 The Role of Operating Systems
- Bridge the “Semantic Gap” between
Hardware and Application
- Three Views of Operating System
1. Abstraction (addresses complexity)
2. Virtualization (addresses sharing)
3. Resource management (addresses performance)
1.2 Organization of Operating Systems
- Structural Organization
- The Hardware Interface
- The Programming Interface
- The User Interface
- Runtime Organization
1.3 Operating System Evolution & Concepts
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Single CPU System
Figure 1-1
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Multiprocessor Systems
Figure 1-2a
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Figure 1-2b
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Multicomputer System
Figure 1-2c
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PC Hardware Organization
Figure 1-7
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Bridging the Semantic Gap
• Hardware capabilities are very low level
– Arithmetic and logical operators
– Comparison of two bit-strings
– Branching, reading, and writing bytes
• User needs to think in terms of problem to be solved
– High-level data structures and corresponding operations
– Simple, uniform interfaces to subsystems,
– Treat programs and data files as single entities
• Use software to bridge this gap
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Language processors (e.g., assemblers, compilers, interpreters).
Editors and text processors, linkers and loaders.
Application programs, utility and service programs.
Operating Systems
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The role of OSs
• Bridge Hardware/Application Gap
– Machine instruction vs. high level operation
• compiler bridges gap
– Linear memory vs. data structures
• compiler bridges gap
– Limited CPU & memory vs. more needed
• OS bridges gap
– Secondary memory devices vs. files
• OS bridges gap
– I/O devices vs. high level I/O commands
• OS bridges gap
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Three views of OSs
• OS is an extended machine
– Principle of abstraction hides complexity
– OS provides high level operations using lower
level operations
• OS is a virtual machine
– Principle of virtualization supports sharing
– OS provides virtual CPU, memory, devices
• OS is a resource manager
– Balance overall performance with individual
needs (response time, deadlines)
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Structural Organization of OSs
• Monolithic vs. Layered
Figure 1-8
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Organization of OSs
• Hardware Interface
– Applications and OS compiled into machine
instructions
– Interrupts and Traps allow OS to seize control
• process management (time-sharing)
• device management (I/O completion)
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Interrupts vs. Traps
Figure 1-9
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Organization of OSs
• Hardware interface (continued)
– Modes of CPU execution
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Privileged/Nonprivileged
SVC (supervisor call) causes trap
Control transferred to OS in privileged mode
OS exits privileged mode when returning to user
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Organization of OSs
• Programming Interface
• Invoking system services
– Library call (nonprivileged)
– Kernel call (privileged)
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Figure 1-8
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Invoking System Services
Figure 1-10
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Organization of OSs
• User interface (cf. Fig. 1-8)
– Text-based shell (e.g. Unix)
• command interpreter
• shell scripts
– Graphics-based GUI (e.g. Mac, MS Windows)
• Windows
• Icons
• Menus
• Pointer
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Organization of OSs
• Runtime organization
– Service is a Subroutine
– Service is an Autonomous Process (“client-server”)
Figure 1-12
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OS Evolution and Concepts
• Early systems
– Bootstrapping
• Batch OSs
– I/O processors
– Interrupts
– Relocatable code (Allows separately compile
programs to be combined without
recompilation)
• Multiprogramming
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Multiprogramming
• Basic problem:
– Some programs are compute-bound, some I/O-bound
– Even “balanced” programs are balance only over time
– No one program can make full use of the system
• Solution: Multiprogramming
– Have more than one active (running) program in
memory at any one time
• Multiprogramming requires
– Bridging the semantic gap
– Sharing resources among different programs
– Hiding from each program the fact of this sharing
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OS Evolution and Concepts
• Multiprogramming Systems
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Overlap CPU and I/O
Protection
Synchronization and Communication
Dynamic Memory Management
(swapping and paging)
• Interactive OSs
– Guaranteed response time
– Time-sharing (quantum)
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OS Evolution and Concepts
• PC and workstation OSs
– GUI
• Real-time OSs
– Deadlines (scheduling)
• Distributed OSs
– Loosely coupled/tightly coupled
– Consistent timeline (logical clocks, time stamps)
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Abstraction
• E.W.Dijkstra, “The Humble Programmer” (1972):
“The purpose of abstraction is not to be vague,
but to create a new semantic level
in which one can be absolutely precise.”
• “abstraction” is created by distinguishing
– Essential characteristics from
Unimportant details
• Build levels (layers) of abstractions:
– What is unimportant detail at one level
is an essential characteristic at a lower one.
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History
• Originally developed by Steve Franklin
• Modified by Michael Dillencourt, Spring, 2009
• Modified by Michael Dillencourt, Summer 2012
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